One approach to the internal fixation of long bone fractures is to insert a relatively flexible intramedullary nail into the medullary canal so that it crosses the fracture site and provides increased rigidity to the fracture fragments. Until recently, such devices have been viewed as gliding splints, allowing the fracture fragments to collapse slightly as weightbearing loads are applied and fracture healing proceeds. Under these conditions, fixation rigidity depends on close-fitting frictional load transmission between intramedullary nail and bone and on adequate contact between the proximal and distal fracture fragments. As a result, intramedullary nails have not traditionally been used with fractures near the bone ends or with severely comminuted central shaft fractures where bone collapse and marked shortening could occur.
In attempts to expand the indications for intramedullary nailing to these fracture types, a number of manufacturers have developed "locking" systems, which are designed to provide secure attachment between the intramedullary nail and the most proximal and distal fracture fragments. Such locking systems prevent collapse of severely comminuted fractures, allow weightbearing relatively early, and increase the torsional, flexural and axial rigidity and strength of the bone-implant system. The availability of these locking systems has resulted in a dramatic increase in the use of intramedullary nailing, to the point that it is the treatment of choice for most long bone fractures of the lower extremity.
Several approaches are used to provide proximal and distal locking of intramedullary nails. These include the use of expanding bolts (U.S. Pat. No. 4,590,930 for an invention of Kurth et al.), fins (West German patent application laid open as number 24 40 045 on Apr. 10, 1975; U.S. Pat. No. 4,519,100 for an invention of Wills et al.), and multiple protruding pins, all operated by screw-type insertions along the length of the nail. (See also the discussion in column 1 of U.S. Pat. No. 4,733,654 for an invention of Marino and columns 1-2 of U.S. Pat. No. 4,697,585 for an invention of Williams.) By far the most popular approach, however, is to employ transverse screws or bolts, which are inserted through transverse holes in the intramedullary nail and corresponding holes drilled in the bone cortices. Such locking screws can be perpendicular or oblique to the longitudinal axis of the bone and can be used singly or in pairs to provide a rigid connection between nail and bone fragment.
In the process of intramedullary nailing, it is common to insert initially, into the medullary canal from the proximal end thereof, a ball-ended guide wire and then to pass this guide wire down the canal to locate the distal fracture fragment. Thereafter a series of flexible intramedullary reamers are passed in succession over the guide wire. The guide wires are also intended to allow withdrawal of the reamer tip in the unlikely case that the reamer breaks during the reaming process. Once reaming is completed, the ball-ended guide wire is usually replaced with a smooth-tipped guide wire and the hollow intramedullary nail is inserted over the guide wire. Once successful positioning of the intramedullary nail is achieved, the guide wire is withdrawn and proximal and distal locking screws are inserted. See U.S. Pat. No. 4,913,137, for an invention of Azer et al.
The prior art has frequently attempted to address the problem of positioning holes, drilled in the most proximal and distal bone fragments, in proper relation to the corresponding holes in the intramedullary nail, so that the locking screws can be inserted to fix the position of the nail vis-a-vis these bone fragments. For proximal locking, it is straightforward to design fixtures that can be used intraoperatively as drill guides for locating the position of the proximal screw or screws. Typically, such devices attach temporarily to the proximal end of the nail, allow the transverse holes to be drilled through a special guide, and are then removed after screw insertion. See U.S. Pat. No. 4,733,654 for an invention of Marino. However, such an approach (described in U.S. Pat. Nos. 4,881,535 for an invention of Sohngen and 4,913,137 for an invention of Azer et al.), has proven unworkable with the distal transverse locking screws. Invariably some twisting and bending of the nail occurs during insertion and thus the geometric relationship between the proximal and distal ends of the nail cannot be determined with certainty.
As a consequence, there have been many attempts to develop locating devices for the distal locking screws that allow holes to be drilled through the bony cortices at the precise location of the distal holes in the intramedullary nail. Approaches have ranged from special radiographic targeting devices (much like bomb sights) to capture mechanisms which depend on prior insertion of the locking screw and a special configuration of the distal end of the nail. For the latter, see U.S. Pat. Nos. 4,817,591 and 4,705,027 for inventions of Klaue. The radiographic approaches are time-consuming, expose the surgeon to excess radiation and do not achieve proper location with absolute certainty. Capture mechanisms have proven unworkable, primarily because of nail deformation and an inability to hit the already inserted screw, and have thus never been marketed. Thus targeting and location of the distal locking screws remain the most time-consuming and problematic phase of the surgical procedure. While highly experienced surgeons eventually learn to accomplish this step successfully, it is considerably more difficult for inexperienced surgeons or for those who do not do intramedullary nailing with considerable frequency.